As examples of therapeutic compounds having a tricyclic nucleus structurally similar to the compound of the present invention, Cyclobenzaprine (The Merck Index, 11th edition, 2719) useful as a muscle relax ant represented by the following formula (II): ##STR2## and Doxepin (The Merck Index, 11th edition, 3425) useful as an antidepressant and an antipruritic agent represented by the following formula (III): ##STR3## are known.
However, Cyclobenzaprine is known to cause adverse reactions such as sleepiness, dizziness, fatigue, thirst, nausea, constipation, and dyspepsia. Doxepin also induces adverse reactions such as sleepiness, thirst, and constipations. These adverse reactions are caused because Cyclobenzaprine or Doxepin have various pharmacological activities such as an activity on central nervous system and an anti-acetylcholinergic activity in addition to their principal activities, i.e., muscle relaxing, anti-depressing activities and anti-histaminic activities.
Accordingly, an object of the present invention is to provide a medicament having an excellent selectivity of increased desired principal activities and reduced side effects by separating various pharmacological activities induced by medicaments such as Cyclobenzaprine and Doxepin.
The inventors of the present invention conducted various studies to achieve the foregoing object and found that the object can be achieved by providing novel tricyclic compounds of the present invention. The inventors also found that the novel tricyclic compounds of the present invention have potent anti-histaminic and anti-allergic activities, and that they are useful as medicaments having excellent selectivities and reduced side effects caused by their anti-acetylcholinergic activity and the like. The present invention was achieved on the basis of these findings.